The Technical Specifications TS101 313 V0.4.2 (1999-02) and TS101 316 V1.1.1 (1999-04) of ETSI (European Telecommunications Standards Institute), describe a network architecture and configurations e.g. for TIPHON (telecommunications and internet protocol harmonization over networks), and illustrate a basic call reference configuration comprising a decomposed gateway. The decomposed gateway includes a media gateway controller and a media gateway controlled by the controller, and eventually a signaling gateway. The media gateway controller provides the connection processing (e.g. call handling) functions for the gateway. The media gateway is a device operating on media and/or control streams.
The decomposing of the gateway into the gateway function and the gateway control is of advantage as it allows an easy change of the control strategy and parameters without necessity of changing the physical gateway structure. Generally, a gateway can be an end point on a network which provides a connection, e.g. real-time, two-way communication, between terminals of two networks, for instance a packet-based network and a circuit-switched network. The information flow between the media gateway and the media gateway controller supports several functions such as creation, modification and deletion of media stream connections across the media gateway; the specification of transformations to be applied to media streams passing through the media gateway; the request of insertion of tones and announcements into media streams; and/or the request of reports and specific actions to be taken upon detection of specified events within the media streams.
Examples of media gateways may include trunk gateways that interface between SCN (Switched Circuit Networks) networks and packet-based networks such as IP (Internet Protocol) networks; “Voice over ATM (Asynchronous Transfer Mode)” gateways which provide interface to an ATM network; access gateways that provide interfaces between “user to network” interfaces and “Voice over IP” networks; residential gateways, i.e. access gateways for a small number of voice terminals that can be co-located with a cable modem or set top box; network access servers; multipoint processing units; IP gateways; fax gateways that may be used to relay Fax Group 3 calls between an IP network and an SCN, and the like. Usually, the media gateway will be physically connected to one or more packet-switched networks and to one or more circuit switched networks. Calls handled by the decomposed gateway may comprise pure data transmission, voice transmission, for instance over a packet-based network, i.e. a network using packet transmission instead of switched circuit network configuration; audio data; video data, combined audio and video data, and the like. The definitions and examples mentioned in the above referenced documents are herewith included into the disclosure contents of the present file.
One or more of these different functions can be co-located and may also be combined with gatekeepers or with other gateways. The signalling gateway may provide the signalling mediation function between the packet-based domain such as the IP domain, and the circuit switched network (SCN) domain. The media gateway provides the media mapping and/or transcoding functions, and maps (e.g. tandem free operation) or transcodes the media in the packet-switched domain (e.g. media transported over RTP/UDP/IP or the like) and media in the SCN domain (e.g. PCM encoded voice, GSM (Global System for Mobile Telecommunications), etc.). The media gateway controller controlling the media gateways receives e.g. SCN signalling information from the signalling gateway and IP signalling from the gatekeeper.
Draft Recommendation H.248/MEGACO issued by ITU (International Telecommunications Union), defines protocols used between elements of a physically decomposed multimedia gateway, e.g. between a media gateway controller (MGC) and a media gateway (MG). This draft recommendation expressly does not define how network elements (such as gateways) work and are to be implemented. A media gateway usually provides two or more terminations e.g. for RTP streams or SCN (Switched Circuit Network) bearer channels. Generally, a termination is a logical entity on a media gateway that sources and/or sinks media and/or control streams. Terminations normally have unique identities (termination identities, i.e. terminationIDs) which are assigned by the media gateway at the time of creation of the terminations. Terminations representing physical entities have a semi-permanent existence. For example, a termination representing a TDM channel might exist for as long as it is provisioned in the gateway.
The terminations are referenced by their assigned termination identities which is an arbitrary schema chosen by the media gateway. TerminationIDs of physical terminations may be provisioned in the media gateway. The terminationIDs may be chosen to have structure. For instance, a terminationID may consist of trunk group and a trunk within the group.
As furthermore mentioned in the draft recommendation H.248/MEGACO, a wildcarding mechanism using two types of wildcards can be used with terminationIDs. The two wildcards are ALL and CHOOSE. The former is used to address multiple terminations at once, while the latter is used to indicate to a media gateway that it must select a termination satisfying a partially specified terminationID. This allows, for instance that a media gateway controller instructs a media gateway to choose a circuit within a trunk group.
As described above, the media gateway chooses the syntax for the terminationIDs so that the terminationIDs may have different kinds of syntaxes or structures. For instance, a terminationID may consist of a trunk group, a trunk within the group and a circuit, or of a trunk group and a trunk within the trunk group. Moreover, the position or sequence of bits referring to e.g. a trunk group may be different from gateway to gateway, or even within a gateway at different times. The media gateway controller may therefore incorrectly specify terminationIDs, e.g. when using a wildcarding schema and defining only part of terminationIDs. A desired connection may then be incorrectly handled by the media gateway.